Early Maya archeologists were a colorful lot, none more colorful than Augustus and Alice Le Plongeon, Mayanists with a simple vision - the Mayas were the founders of world civilization.

History has not treated the Le Plongeons well. Their contemporaries wrote them off as cranks. Modern critics have called them misguided romantics. Lawrence Gustave Desmond and Phyllis Mauch Messenger's lavishly illustrated biography, ''A Dream of Maya,'' attempts a more dispassionate assessment. It reveals a husband and wife torn between the demands of sober fieldwork and those of a more mystical past.

Augustus Le Plongeon graduated from the Ecole Polytechnique in Paris in 1845 when he was 19 years old. He and a friend bought a yacht and sailed to Chile, where they were shipwrecked. Hearing of the gold rush, Le Plongeon sailed to the United States and set up as an engineer and surveyor (he laid out the plan of Marysville, Calif., just then being built, and thus became a successful land agent). He became a Mayanist at a time when almost anyone with the money to travel could become an archeologist. Under the circumstances, Le Plongeon's qualifications were as good as anyone's. He went to Maya country with a colorful background as a teacher, traveler, speculator and photographer. He had cut his archeological teeth in Peru, photographing Inca ruins for Ephraim Squier, the famous student of the Mound Builders in the Ohio and Mississippi valleys. In 1873, at the age of 47, the ingenious and ever-inquisitive Le Plongeon married his young English wife, Alice, and arrived in the Yucatan to probe the mysteries of Maya civilization.

No one could accuse the Le Plongeons of not being thorough. They learned Yucatec Maya, better to communicate with the modern Indians and interpret ancient glyphs. In several long field seasons they explored Uxmal, Chichen Itza and many other smaller sites, photographing, recording, clearing buildings and sometimes excavating. But unfortunately Augustus Le Plongeon committed a cardinal sin of archeological research. He came to the Yucatan with preconceived ideas, with what he undoubtedly considered a higher mission - to show that Maya country was the cradle of all human civilization.

Augustus and Alice Le Plongeon soon displayed a split personality in the field. Their recording and excavation methods were as good as, if not better than, those of archeologists anywhere. The photographer in Le Plongeon went to extraordinary lengths to eliminate distortion from his prints. A pioneer of negative film, he experimented with stereoscopic photographs with marked success. No contemporary archeologist could describe Augustus and Alice Le Plongeon as irresponsible fieldworkers. Had they been content merely to record their findings, the Le Plongeons would have become respected members of the scholarly community. But their passion for romantic speculation turned sober scholarship into fantasy.

Isolated for months at Chichen Itza during a period of serious political unrest, the Le Plongeons brooded on the mysterious ruins around them. They traced bas-reliefs in the Lower Temple of the Jaguars and were convinced they represented the history of a single Maya generation. Soon conviction became obsession. In the steamy heat of the Yucatan, the Le Plongeons wrote an account of Queen Moo from the undeciphered glyphs, naming her after the Maya word for macaw, her totem. Her brother was Prince Chaacmol, ''powerful warrior.'' After many intrigues and murders, Moo was forced to flee to Egypt, where she was recognized as a long-lost sister of the Pharaoh. Thus, the Le Plongeons argued, Egyptian civilization had been originated by the ancient Mayas.

Sometime later, rudimentary archeological instinct led Augustus Le Plongeon to a small mound where he found a large sculpture of a reclining male. The legend of Moo came to archeological life; the sculpture could only be the figure of Prince Chaacmol, the youngest brother and consort of the Queen. The legend of Queen Moo and Chaacmol was to preoccupy the Le Plongeons for the rest of their lives.

By the time the exhausted couple returned to the United States for the last time in 1884, Moo and Chaacmol were already a joke in archeological circles. Quite apart from Augustus Le Plongeon's impetuous and quarrelsome personality, his diffusionist views of Maya civilization conflicted with the conventional scientific view that the American Indians had originated in Asia. A generation earlier, he might have received a more sympathetic hearing, for legends of Mound Builders and ancient voyagers to the Americas were in vogue. But now he confronted a scientific establishment made up of veterans of field expeditions in the American Far West who based their thinking on more sober assessments of the past. The Le Plongeons were ignored, even ostracized. Their response was to withdraw into their own world, searching for every shred of evidence they could find to prove the Egyptian connections with Maya civilization, and with Freemasonry into the bargain.

In ''Queen Moo and the Egyptian Sphinx'' (1896), Augustus Le Plongeon presented the Moo story in all its bewildering complexity, not as a step-by-step interpretation of individual glyphs but as a morass of broad interpretations and mystical statements. Inevitably, even sympathetic reviewers castigated his extravaganza. Alice Le Plongeon turned to fiction to express her ideas. Perhaps the Le Plongeons thought of themselves as Moo and the warrior prince Chaacmol reincarnated. Undoubtedly, their interpretations of Maya civilization welled up from their romantic subconscious.

As the authors point out in their clear but superficial biography, it is difficult to be lukewarm about the Le Plongeons. By all accounts they were a warm, likable couple, highly intelligent people with hyperactive minds. But they were paranoid and quarrelsome, especially toward those who opposed their views.

At this point, Mr. Desmond, a research associate with the California Academy of Sciences, and Ms. Messenger, assistant to the director of the Institute of International Studies at the University of Minnesota, leave us in academic midair. What scientific archeologist has not witnessed similar behavior among the Le Plongeons' pseudoarcheological descendants in the 1980's? The arena may now be outer space or lost continents off the continental shelf, but all the symptoms of pseudoscience are the same. What causes apparently rational, thinking people to turn obsessive about the past, to pursue theories about the past that fly in the face of all known scientific facts? It is a pity that the authors did not use the case of these fascinating, yet tragic, Mayanists to examine the lasting and important phenomenon of the obsessive archeologist with the attention it merits. We have much to learn from this bizarre, yet compelling, couple.